<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .outer{
            width: 1000px;
            height: 900px;
            background-color: #888888;
            margin: 0 auto;
            display: flex;
            box-sizing: border-box;
            /*align-items: ;*/
        }
        .inner{
            width: 200px;
            height: 200px;
            background-color: skyblue;
            border: 1px solid black;
        }
        .inner2{
            height: 300px;
        }
        .inner3{
            height: 100px;
        }
    </style>
</head>
<body>
<div class="outer">
    <div class="inner inner1">1</div>
    <div class="inner inner2">2</div>
    <div class="inner inner3">3</div>
    <div class="inner ">4</div>
    <div class="inner ">5</div>
    <div class="inner ">6</div>
    <div class="inner ">7</div>
    <div class="inner ">8</div>
    <div class="inner ">9</div>
    <div class="inner ">10</div>
    <div class="inner ">11</div>
</div>
</body>
</html>